Contrasting the impacts of the 1997–1998 and 2015–2016 extreme El Niño events on the East Asian winter atmospheric circulation

Abstract

This study investigates how the Indian Ocean Dipole (IOD) modulated the influence of the 1997–1998 and 2015–2016 El Nino events on the East Asian winter atmospheric circulation. Due to the extreme IOD in the fall of 1997, the tropical Indian Ocean (TIO) displayed higher sea surface temperature (SST) anomalies in the western basin than in the eastern basin during the following winter. As a result, the Walker circulation weakened in the TIO and tropical Pacific, leading to a zonal rainfall dipole in the Indo-Western Pacific (IWP), which triggered a wave train pattern over East Asia with positive geopotential height anomalies in the upper-level troposphere over northeastern China and Japan during the winter of 1997–1998. In contrast, there was no IOD in the fall of 2015, and the winter rainfall anomaly in the western TIO was weak that year. The geopotential height anomalies were negative around northeastern China and the Sea of Japan—the opposite of those during the winter of 1997–1998. Comparing the historical El Nino events with the high IOD index and low IOD index indicates that the IOD is a crucial contributor to the dipole rainfall in the IWP and, thus, the circulation anomalies in East Asia.